To add on this, its not just Fent, it's all opiates and it comes in two major forms IIRC
The first is respiratory depression. Which is a gradual shift where you don't breath deeply and quickly enough, and your brain doesn't read that, so you gradually lose consciousness and die.
The second is respiratory distress from fluid in the lungs. Basically, your body's lipoproteins (lung wd40) are normally meant to keep things nice and slippery, but the opiates cause it to overproduce and flood the lungs with fluid. This is basically choking on your own lungs.
To be fair, you can be experiencing this and not die. Nor do you have to be "overdosing" to suffer from minor version of it. Think of a milk carton thats 20% full with all the milk on the bottom. Now tip it on its side. How much milk is now covering the jug? nearly 40%.
TBH if I was the prosecutor I'd go with this. Argue that basically anyone with fluid in the lungs would have the exact same issue. Find a position meant for people suffering respiratory distress.
Fortunantly, last I heard there was totally, 0 evidence of Floyd taking drugs. What? Toxicology? Drugs on him? Bro that's the police bro you can't trust that info bro.